Power supplies for electronic devices are divided into two general types. In one type, known as a linear power supply, the line alternating current is transformed to an appropriate voltage, rectified and filtered by capacitors and inductance coils. A linear regulator may then be provided in the output circuit to maintain a constant output voltage. Although this type of power supply is widely used, it requires heavy transformers and large capacitors, and it has a relatively low power transform efficiency.
In a second type of conventional power supply, known as a switched power supply, the line alternating current is rectified and filtered and supplied to an inverter circuit. The inverter switches the filtered signal on and off at a high rate to generate a high frequency squarewave. An output transformer then converts the squarewave to the desired voltage level, and the resulting current is passed through a rectifying network and filters to produce a direct current output.
This latter type of power supply uses lighter components and has a relatively high transform efficiency. The present invention provides an improved power supply of the second type in the form of a synchronous converter, which is relatively simple in its construction and which exhibits a high power factor and enhanced hold-up.